JPH07323355A - Continuous casting method and belt type continuous casting apparatus - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a continuous casting method and a belt type continuous casting apparatus capable of performing high-speed casting while preventing residual bulging deformation of a slab. [Constitution] When continuously casting molten metal at a casting speed of 2.5 m / min or more, a distance L between upper and lower rolls of a plurality of pairs of support rolls directly under the mold is 220 mm or less and a casting speed V (m / min) Therefore, the continuous casting method prevents vertical vibration of the molten metal surface in the mold by guiding the slab to 506 · V ^−1/2 or less. Also, a pair of endless rotating belts and a pair of belts sandwiched between the descending parts
In a belt-type continuous casting facility in which the mold part is formed by a pair of side dams, the slab is supported below the mold part by a support roll having a distance between the upper and lower rolls of 180 mm or less to prevent bulging residue of the slab. A belt type continuous casting machine is also proposed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous casting method and a belt type continuous casting apparatus.

[0002]

2. Description of the Related Art Continuous casting of steel is operated, for example, by a casting machine shown in FIG. In FIG. 1, reference numeral 1 denotes a fixed vibration type or movable type mold which holds a predetermined cross section, and below the mold part 1, the cast piece 3 is rotated to support the unsolidified cast piece 3. A plurality of pairs of support rolls 2 and 5 are arranged with a predetermined distance L between the upper and lower roll axes.

Molten steel 3a is continuously poured into the mold part 1 from a tundish and a pouring nozzle (not shown) above the mold 1 to form a solidified shell 3b cooled in the mold 1. The piece 3 is pulled out from below at a certain casting speed. This unsolidified slab 3 is supported by support rolls 2 and 5 from both sides to maintain its thickness t in order to reduce the deformation (bulging) of the solidified shell 3b due to the static pressure of molten steel to a certain amount or less, and to keep it downward. Send out. In the figure, UBP is a straightening roll for straightening the slab 3 from the curve horizontally, and 10 is a driving pinch roll for pulling out the slab, which is arranged at the end of the continuous casting machine.

The bulging amount δ is expressed by the following equation.

Δ = A · (PL ³ / S ³ ) where P is the static pressure of molten steel, L is the distance between the center axes of the support rolls, S is the shell thickness, and A is the proportional constant.

Further, the shell thickness S is expressed by the following equation.

S = k (D / V) ^1/2 where k is a proportional constant, D is a casting length, and V is a casting speed.

From both equations, the bulging amount δ is represented by the following equation for the same casting length.

Δ = B · (L ³ V ^3/2 ) where B is a proportional constant.

As described above, the bulging amount increases as the distance L between the upper and lower roll axes (hereinafter referred to as the distance L between rolls) increases and the casting speed V increases.

As shown in FIG. 5 showing the bulging of the cast slab 3,
In the slab 3, the solidified shell 3b swells between the support rolls 2 (unsupported zone) due to the static pressure P of the mold part 1. Normally, when the casting speed is slow, the solidified shell 3b becomes thick and the bulging amount δ is small. Therefore, the deformation of the solidified shell becomes the deformation within the elastic deformation, the bulging deformation does not remain, and the bulging amount δ does not change with time.

However, as the casting speed increases, the solidified shell 3b becomes thinner and the bulging amount δ increases, and the solidified shell 3b plastically deforms beyond a certain limit bulging amount. Therefore, bulging deformation remains, and the deformation of the slab changes with time.

Therefore, as shown by the two-dot chain line in FIG. 5, when the bulging portion comes to the position of the next support roll 2, the thickness t becomes as thin as t ₁ and the volume of this portion decreases.
The molten metal level in the mold 1 rises, and the molten level 3c vibrates up and down every time the slab with the remaining bulging passes through each of the support rolls 2, making it difficult to control the level of the molten level 3c.

When vertical vibration of the molten metal surface 3c occurs,
It becomes difficult to control the level of the molten metal surface 3c and it becomes impossible to continue casting. Further, if the above bulging remains on the surface of the slab 3, the flatness thereof deteriorates, the thickness becomes uneven, and the quality remarkably deteriorates.

On the other hand, a schematic structure of an example of a conventional belt type continuous casting apparatus is shown in FIG. 6. In FIG. 6, 52 is a pair of metal belts, which are wound around a roll 53 and both belts are wound. It rotates endlessly with a pair of side dams 54 composed of short piece block connecting bodies sandwiched at both ends of the descending part of 52, and by this belt 52 and side dams 54,
A mold part 51 is formed.

Reference numeral 55 is a molten metal level detector, which is a mold part 51.
Is disposed on the upper part of the. Below the mold part 51,
A plurality of support rolls 2 that rotate as the slab 3 descends to support the unsolidified slab 3 are arranged in a row with a predetermined roll-to-roll distance L.

The molten steel 3a is melted by a melt level detector 55 from a tundish and a pouring nozzle (not shown) above the mold part 51 to the mold part 51 where the opposing belt 52 and side dam 54 descend. The molten metal is continuously poured while detecting the surface 3c, and the slab 3 on which the solidified shell 3b is formed is discharged from below. This unsolidified slab 3 is supported by the support rolls 2 from both sides, the thickness t thereof is maintained, and the slab 3 is discharged downward.

As shown in FIG. 7, which shows the bulging of the cast piece 3 in FIG. 6, the solidified shell 3b of the cast piece 3 swells due to the static pressure P in the mold 51 between the fulcrums of the upper and lower support rolls 2. However, usually, when the casting speed is slow, the solidified shell 3b becomes thick and the bulging amount δ becomes small, and the bulging portion of the shell 3b is plastically deformed by both support rolls 2 therebelow, and the original thickness t Restore to.

However, in this belt type continuous casting apparatus,
Since a high-speed casting with a casting speed of 10 m / min is required, the slab 3 descends at a high speed, and the roll distance L of the support roll 2 at the slab outlet of the mold part 51 becomes, for example, 190 to 250 mm. Since the setting is wide, the solidification shell 3b becomes thin as shown in FIG. 7, and the bulging amount δ
Grows larger. The molded portion 51 is the belt 5
Since 2 is thin and the heat removal effect is high, the temperature of the solidification shell 3b is as low as 700 to 800 ° C. and its hardness is high, and the thickness t
Will not be restored.

Therefore, when the bulging portion comes to the position of the lower support roll 2 as shown by the chain double-dashed line in FIG. 7, the thickness t becomes as thin as t ₁ and the volume of this portion decreases, so that the mold portion When the molten steel 3a in 51 rises and the slab 3 with the remaining bulging passes through each support roll 2, the molten metal surface 3c moves up and down, which makes it difficult to control the molten metal surface 3c.

According to the experiment, as shown in FIG. 8, medium carbon steel (C = 0.16%) with the roll distance L = 210 mm.
When casting is performed, the bulging amount δ remains over 1 mm at a casting speed of about 6.5 m / min, and vibration of the molten metal surface 3c occurs. When L = 190 mm, the casting speed is about 8 m / min for medium carbon steel and about 8.5 m / min for low carbon steel (C = 0.05%) and high carbon steel (C = C = 0.05%). 0.27
%), The bulging amount δ remains over 1 mm at a casting speed of about 9.5 m / min, and vibration of the molten metal surface 3c occurs.

As explained above, the bulging amount δ is 1
It can be considered that the bulging remains and the vibration of the molten metal surface 3c occurs when it exceeds mm. Further, when the above bulging remains on the surface of the cast slab 3, the flatness thereof deteriorates,
The thickness is uneven and the quality is remarkably deteriorated.

[0023]

SUMMARY OF THE INVENTION The present invention has been proposed in order to solve the problem of bulging residue found in the above-mentioned conventional continuous casting method. It is an object of the present invention to provide a continuous casting method that facilitates surface level control, improves the quality of a slab, and enables high-speed casting.

Further, the present invention has been proposed to solve the problem of bulging occurring in the conventional belt type continuous casting apparatus, and prevents the bulging from remaining in the cast slab to control the molten metal surface. An object of the present invention is to provide a belt-type continuous casting device that can be easily made to improve the quality of a cast piece.

[0025]

In order to solve the above-mentioned problems in the continuous casting method, the present invention provides continuous casting of molten metal at a casting speed of 2.5 m / min or more.
Melting in the mold by setting the roll distance L of the plural pairs of support rolls directly under the mold to 220 mm or less and the casting speed V (m / min) to ^{506.V -1/2} or less to guide the slab. Provided is a continuous casting method for preventing vertical vibration of a molten metal surface.

The present invention can be applied to both a movable mold such as an endless track or belt in which the mold part moves in synchronization with the slab and a fixed vibration mold in which the mold part does not synchronize with the slab.

According to the experiment, as shown in FIG. 2 in which the relationship between the roll distance L and the casting speed V indicates the occurrence of fluctuations in the molten metal level in the mold, when the casting speed is set to 2.5 m / min or more, the roll distance changes. If it is not less than 220 mm, vertical vibration of the molten metal surface 3c will always occur.

When casting is performed with the roll distance L = 210 mm, the vertical velocity of the molten metal surface 3c occurs at a casting speed of about 6.0 m / min. Further, when L = 190 mm, the casting speed is about 8 m / min, and when L = 160 mm, the casting speed is about 12 m / min, and vertical vibration of the molten metal surface 3c occurs.

As a result, the distance L between rolls is set to L ≦ 506 · V ^{−1 / 2} and L ≦ 22 depending on the casting speed V.
2.5 m / by performing continuous casting by filling 0
The amount of bulging generated between the support rolls of the solidified shell of the slab thinned by high-speed casting for more than a minute is kept below the allowable value, the deformed shape is prevented from remaining due to plastic deformation of the shell, and vertical vibration of the molten metal surface is prevented. To prevent. That is, unless the distance L between the rolls is satisfied with L ≦ 506 · V ^−1/2 and L ≦ 220, the bulging remains when the bulging amount δ exceeds a certain limit value, and vertical vibration of the molten metal surface 3c occurs.

As described above, according to the continuous casting method of the present invention, the fluctuation of the molten metal surface can be prevented and stable casting can be realized, and no bulging remains in the cast slab.

Next, according to the present invention, a mold portion comprising a pair of lowering portions of a pair of belts wound around a plurality of rolls and rotating endlessly, and a pair of side dams sandwiched between both ends of the lowering portion of the belt, and this mold. In order to solve the above problems in the belt type continuous casting apparatus having a slab support device composed of a plurality of support rolls supporting the slab discharged downward from, the distance between the upper and lower rolls of the support roll is at least directly below the mold. Adopt a structure in which the part is formed to be 180 mm or less. In the present invention, the section of the support roll immediately below the mold where the distance between the upper and lower rolls is 180 mm or less can be set to 3000 mm, for example.

The pair of belts and the pair of side dams are rotated, the molten metal is continuously poured into the mold portion and cooled, and the continuously cast slab is discharged downward from the mold portion. In the belt type continuous casting apparatus according to the present invention, this slab is supported from both sides by support rolls having a distance between the upper and lower rolls shortened to 180 mm or less, and bulging occurs between the support rolls of the solidified shell of the slab thinned by high speed casting. The amount is kept below the allowable value and the plastic deformation of the shell restores it to a predetermined thickness to prevent residual bulging.

[0033]

Embodiments of the continuous casting method and belt type continuous casting apparatus according to the present invention will be specifically described below with reference to the drawings. First, FIG. 1 shows an embodiment of a continuous casting method according to the present invention.
This will be specifically described with reference to FIG.

In FIG. 1, reference numeral 2 denotes a support roll having a small diameter, which faces the first segment portion 4 immediately below the mold portion 1 at a predetermined interval and is arranged in a row with a required roll distance L in the vertical direction. Has been done. A large-diameter (200 mm diameter) support roll 5 is provided in the second segment 6 in a row. The support roll is 1 larger than the maximum slab width to be cast
The length of the slab is set to be long by 00 to 200 mm, and the slab is clamped and supported by the pair of rolls over the entire width of the slab.

Molten steel 3a is continuously poured into the mold 1 from a tundish and a pouring nozzle (not shown) above the mold 1 to form a solidified shell 3b cooled in the mold. 3 is pulled out from below at a certain casting speed. While this unsolidified slab 3 is cooled by a cooling spray (not shown), it is supported by the support rolls 2 from both sides, its thickness t is maintained, and it is sent out downward.

(Operation Example 1) Using the continuous casting machine having the above construction, molten steel composition: medium carbon steel (C = 0.16%, Si =
0.40%, Mn = 0.8%, P = 0.02%, S =
0.01%) 340Ton and low carbon steel (C = 0.06)
%, Mn = 0.3%, P = 0.02%, S = 0.01
%) 340Ton was continuously cast under the following conditions.

Mold type: fixed mold, slab size:
70mm thickness x 1500mm width, support roll 2 diameter: 1
95mm, distance L between support rolls 2 L: 220m
m, number of support rolls 2 installed: 8.

(1) Casting speed 2.5 m / min, 506 V
^-1/2 = 320 (A in Fig. 2) and 4m / min, 506V
^When casting was performed at ^-1/2 = 253 (B in Fig. 2), vertical vibration of the molten metal surface did not occur, and stable casting could be continued. Further, the cast piece was also obtained with a uniform thickness.

(2) 6 m / min, 506 · V ^−1/2 = 207
In the case of casting (E in FIG. 2), vertical vibration of the molten metal surface occurred and casting could not be continued.

(Operation Example 2) A molten steel composition: medium carbon steel (C = 0.
16%, Si = 0.40%, Mn = 0.8%, P = 0.
02%, S = 0.01%) 340Ton and low carbon steel (C = 0.06%, Mn = 0.3%, P = 0.02%,
340 Ton (S = 0.01%) was continuously cast under the following conditions.

Mold type: Twin belt type moving mold, slab size: 50 mm thickness x 1300 mm width, support roll 2 diameter: 175 mm, support roll 2 roll distance L: 190 mm, number of support rolls 2 installed: 9 .

(1) Casting speed 6 m / min, 506 · V ^-1/2
= 207 (C in FIG. 2), the vertical vibration of the molten metal surface did not occur, and stable casting could be continued.
Further, the cast piece was also obtained with a uniform thickness. (2) On the other hand, when casting was performed at 8 m / min and 506 · V ^−1/2 = 179 (F in FIG. 2), vertical vibration of the ^molten metal surface occurred,
The casting could not be continued.

(Operation Example 3) Using the continuous casting machine (mold type: moving mold) having the same configuration as in Operation Example 1, the molten steel composition:
Medium carbon steel (C = 0.16%, Si = 0.40%, Mn =
0.8%, P = 0.02%, S = 0.01%) 340T
on and low carbon steel (C = 0.06%, Mn = 0.3%,
For each of 340 Ton (P = 0.02%, S = 0.01%), continuous casting was performed under the following conditions.

Slab size: 50 mm thickness × 1300 mm width, support roll 2 diameter: 135 mm, support roll 2 roll-to-roll distance L: 160 mm, number of support rolls 2 installed: 12.

(1) Casting speed 10 m / min, 506 V
^When casting was performed at ^-1/2 = 160 (D in Fig. 2), vertical casting of the ^molten metal surface did not occur, and stable casting could be continued. Further, the cast piece was also obtained with a uniform thickness. (2) When casting was performed at 12 m / min and 506 · V ^−1/2 = 146 (G in FIG. 2), vertical vibration of the molten metal surface occurred and the casting could not be continued.

Next, one embodiment of the belt type continuous casting apparatus according to the present invention will be specifically described with reference to FIGS.

In these figures, the same elements as those of the conventional device shown in FIG. 6 are denoted by the same reference numerals as those of the conventional device, and duplicated explanations are omitted.

In FIG. 3, reference numeral 2 denotes a small-diameter support roll, which faces the first segment portion 4 in a section 3000 mm directly below the mold portion 51 at a predetermined interval and forms a required roll-to-roll distance L in the vertical direction. It is lined up. Reference numeral 5 denotes a large-diameter support roll, which is arranged in a row on the second segment portion 6. The support roll is 1 larger than the maximum slab width to be cast
The length of the slab is set to be long by 00 to 200 mm, and the slab is clamped and supported by the pair of rolls over the entire width of the slab.

The molten steel 3a is fed from the tundish and the pouring nozzle (not shown) above the mold portion 51 to the mold portion 51 where the belt 52 and the side dam 54 facing each other are descended by the molten metal surface detector 55. Slab 3 formed by solidifying shell 3b by continuously pouring while detecting
Is discharged from below. While this unsolidified slab 3 is cooled by a cooling spray (not shown), it is supported by the support rolls 2 from both sides, its thickness t is maintained, and it is discharged downward.

In the experiment using the equipment of FIG. 3, as shown in FIG. 4, when the casting speed is 10 m / min, the roll distance L is about 180 mm for high carbon steel and the roll distance L is about 165 mm for medium carbon steel. With low carbon steel, the distance L between rolls is about 170 mm, and the bulging amount b can be suppressed to about 1 mm, so that no bulging remains on the slab 3. Therefore, the molten metal surface 3c in the mold part 51 is stabilized.

[0051]

As described above, in the continuous casting method according to the present invention, the distance L between the support rolls immediately below the mold part is set to satisfy L ≦ 506 · V ^−1/2 and L ≦ 220. By providing and casting, the bulging amount between the support rolls of the shell of this slab thinned by high-speed casting of 2.5 m / min or more is kept below the limit value, residual bulging is prevented, and molten surface fluctuation By preventing the occurrence of, it is possible to realize stable casting according to the casting speed. Further, since no bulging remains on the slab, the accuracy of the thickness and flatness of the slab can be improved.

Further, according to the belt type continuous casting apparatus of the present invention, the roll distance between the support rolls in the portion directly below the mold portion, for example, in the section 3000 mm directly below the mold portion, is 18 mm.
By forming the slab to have a thickness of 0 mm or less, the bulging amount between the support rolls of the shell of this slab thinned by high-speed casting can be maintained at an allowable value or less, and residual bulging can be prevented.

Therefore, it is possible to prevent the vibration of the molten metal surface in the mold portion, and it is possible to easily control the molten metal surface. Also, since there is no residual bulging on the slab,
The accuracy of its thickness and flatness can be improved.

[Brief description of drawings]

FIG. 1 is a side view showing a schematic configuration of an example of a continuous casting apparatus for carrying out the method of the present invention.

FIG. 2 is a graph showing a situation of occurrence of fluctuations in a molten metal level in a mold in relation to a distance L between rolls and a casting speed V.

FIG. 3 is a side view showing a schematic configuration of a belt-type continuous casting apparatus which is an embodiment of the present invention.

FIG. 4 is a diagram showing an experimental result of a bulging amount in the belt type continuous casting apparatus of FIG.

FIG. 5 is an explanatory view showing bulging of a cast piece.

FIG. 6 is a side view showing a schematic configuration of an example of a conventional belt type continuous casting device.

FIG. 7 is an explanatory view showing bulging of the cast piece in FIG. 6.

FIG. 8 is a graph showing the relationship between the distance between support rolls, steel type, casting speed, and bulging amount by experiments.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Mold part 2 Support roll 3 Cast piece 3a Molten steel 3b Solidification shell 3c Molten surface 4 First segment part L Roll distance δ Bulging amount t Cast piece thickness 10 Driving pinch roll 51 Mold part 52 Belt 53 Roll 54 Side dam UBP Straightening roll

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hiroshi Nakajima 4-6-22 Kannon Shinmachi, Nishi-ku, Hiroshima City Mitsubishi Heavy Industries, Ltd. Hiroshima Research Laboratory (72) Shinji Matsuo 1st Nishinozu, Oita City, Oita Prefecture Shin Nippon Steel Co., Ltd. Oita Steel Works (72) Inventor Noriyuki Kanai No. 1 Nishinozu, Oita City, Oita Prefecture New Japan Steel Co., Ltd. Oita Steel Works (72) Inventor Satoshi Horioka Oita City, Oita Prefecture Oita City No. 1 No. 1 Nippon Steel Co., Ltd. Oita Steel Co., Ltd. (72) Inventor Keiichi Katahira 20-1 Shintomi, Futtsu City, Chiba Nippon Steel Co., Ltd.

Claims (2)

[Claims] 1. When continuously casting molten metal at a casting speed of 2.5 m / min or more, a distance L between the upper and lower roll axes of a plurality of pairs of support rolls immediately below the mold is 220 mm or less and a casting speed V (m / m). The continuous casting method is characterized by preventing vertical vibration of the molten metal surface in the mold by guiding the slab to 506 · V ^−1/2 or less in relation to the above. 2. A molding section comprising a pair of lowering portions of a belt wound around a plurality of rolls and rotating endlessly, and a pair of side dams sandwiched between both ends of the lowering portion of the belt.
And a slab support device comprising a plurality of support rolls for supporting the slabs discharged downward from the mold part, and a distance L between the upper and lower roll axes of the support rolls.
180 at least directly below the mold section.
A belt-type continuous casting machine characterized by being less than mm.